This invention relates to acetylenic polysilanes composed of [RSi] and [R.sub.2 Si] units where there are present 0 to 60 mole percent [R.sub.2 Si] units and 40 to 100 mole percent [RSi] units and to acetylenic polysilanes composed of [RSi], [R.sub.2 Si], and [R"Si] units where there are present 0 to 40 mole percent [R.sub.2 Si] units, 0.1 to 99.9 mole percent [RSi] units, and 0.1 to 99.9 mole percent [R"Si] units, where R is an alkyl radical containing 1 to 8 carbon atoms, where R" is selected from the group consisting of alkyl radical containing at least six carbon atoms, phenyl radicals, and radicals of the formula A.sub.3 Si(CH.sub.2).sub.z -- wherein A is selected from the group consisting of hydrogen and alkyl radicals containing 1 to 4 carbon atoms, and z is an integer greater than or equal to 1, and where the remaining bonds on silicon are attached to other silicon atoms and acetylenic groups of the formula --(CH.sub.2).sub.w C.tbd.CR' where w is an integer from 0 to 3 and where R' is hydrogen, an alkyl radical containing 1 to 6 carbon atoms, a phenyl radical, or an --SiR"'.sub.3 radical wherein R"' is an alkyl radical containing 1 to 4 carbon radicals. These acetylenic polysilanes are prepared by reacting a halogen-containing polysilane composed of [RSi] and [R.sub.2 Si] units, where there are present 0 to 60 mole percent [R.sub.2 Si] units and 40 to 100 mole percent [RSi] units, or a halogen-containing polysilane composed of [RSi], [R.sub.2 Si], and [R"Si] units, where there are present 0 to 40 mole percent [R.sub.2 Si] units, 0.1 to 99.9 mole percent [RSi] units, and 0.1 to 99.9 mole percent [R"Si] units, with an acetylenic Grignard reagent or acetylenic lithium compound.
The acetylenic polysilanes of this invention may be rendered infusible by reaction with certain organometallic compounds under an inert atmosphere or by exposure to UV irradiation in an inert atmosphere prior to pyrolysis to form ceramic materials. Such cure mechanisms can result in ceramic materials containing only limited amounts of oxygen.
Bujalski et al. in two copending U.S. patent applications entitled "A Method of Producing Silicon Carbide Preceramic Vinyl-containing Polymers" Ser. No. 94,347 and "An Improved Method of Producing Silicon Carbide Preceramic Vinyl-containing Polymers" Ser. No. 93,434 describe vinyl-containing polysilanes which can be converted into ceramic materials by pyrolysis at elevated temperatures.
Baney et al. in U.S. Pat. No. 4,310,651 (issued Jan. 12, 1982) disclosed polysilanes composed of [CH.sub.3 Si] and [(CH.sub.3).sub.2 Si] units where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and chlorine atoms or bromine atoms. The polysilane was converted to a beta-silicon carbide-containing ceramic at elevated temperatures (about 1400.degree. C.).
Baney et al. in U.S. Pat. No. 4,298,559 (issued Nov. 3, 1981) prepared polysilanes composed of [CH.sub.3 Si] and [(CH.sub.3).sub.2 Si] units where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and additional alkyl radicals of 1 to 4 carbon atoms or phenyl radicals. Upon heating these polysilanes were converted into silicon carbide-containing ceramics in high yields.
Baney et al. in U.S. Pat. No. Re. 31,447 (reissued Nov. 22, 1983) disclosed polysilanes composed of (CH.sub.3 Si] and [(CH.sub.3).sub.2 Si] units where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and alkoxy radicals containing 1 to 4 carbon atoms or phenoxy radicals. Silicon carbide ceramics were obtained by firing these polysilanes to elevated temperatures.
Baney et al. in U.S. Pat. No. 4,314,956 (issued Feb. 9, 1982) disclosed polysilanes composed of [CH.sub.3 Si] and [(CH.sub.3).sub.2 Si] units where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to silicon and amine radicals of the general formula --NHR.sup.v where R.sup.v is a hydrogen atom, an alkyl radical of 1 to 4 carbon atoms or a phenyl radical. A silicon carbide ceramic was obtained by firing this polysilane to an elevated temperature under an inert atmosphere.
The just discussed U.S. Pat. Nos. 4,310,651, 4,298,599, Re. 31,447, and 4,314,956 are hereby incorporated by reference. These polysilanes are further discussed in Baney et al. Organometallics, 2, 859 (1983).
West in U.S. Pat. No. 4,260,780 (issued Apr. 7, 1981) prepared a polysilane composed of [(CH.sub.3).sub.2 Si] and [CH.sub.3 (C.sub.6 H.sub.5)Si] units by the sodium metal reduction of dimethyldichlorosilane and methylphenyldichlorosilane. The resulting polysilanes had very high softening points (&gt;280.degree. C.).
West et al. in Polym. Prepr., 25, 4 (1984) disclosed the preparation of a polysilane composed of [CH.sub.3 (CH.sub.2 .dbd.CHCH.sub.2)Si] and [CH.sub.3 (C.sub.6 H.sub.5)Si] units by the sodium metal reduction of allylmethyldichlorosilane and methylphenyldichlorosilane. These polysilanes were rapidly gelled by irradiation with ultraviolet irradiation.
Seyferth et al. in U.S. Pat. No. 4,639,501 (issued Jan. 27, 1987) prepared preceramic polymers by reacting a methylpolysilane of the general formula [(RSiH).sub.x (RSi).sub.y ] .sub.n with an organosilicon compound having at least two vinyl groups of the general formula [R.sub.2 (CH.sub.2 =CH)Si] .sub.2 Y, where, for example, Y is O, S, NH, NR, or is absent, using either UV irradiation, thermal energy, or catalysts.
It has now been determined that polysilanes composed of [RSi] and [R.sub.2 Si] units or polysilanes composed of [RSi], [R.sub.2 Si], and [R"Si] units which contain acetylenic groups may be prepared in good yield. The presence of acetylenic groups in the polysilanes is confirmed experimentally. These acetylenic polysilanes may be pyrolyzed at elevated temperatures in an inert atmosphere to produce silicon carbide-containing ceramics. The acetylenic polysilanes may be cured, and thus rendered infusible, prior to pyrolysis either by reaction with certain organometallic compounds or by exposure to ultraviolet irradiation.